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MikeDobbs 05-18-2012 09:33 AM

Radiant Heating on a Concrete Slab
Hi everyone. I'm redoing a bathroom and intend to lay down ceramic tile with electric radiant heating underneath. My concern is this: the bathroom is on a concrete slab, and I'm worried that the slab may pull too much heat from the system rendering the radiant heating ineffective or very expensive to run.

The manufacturer seems to suggest laying down 1/4 inch cork on top of a slab for thermal insulation, but this seems like it may cause an issue with the floor not being sold enough and tiles cracking?

If anyone has any experience with this issue, and can make some recommendations I would really appreciate it.

I live in Long Island, NY, so we have reasonably cold weather for several months out of the year.


warmsmeallup 05-21-2012 02:17 PM

Are you looking for a floor warming system or a primary (only source) heating system for the bathroom?

MikeDobbs 05-21-2012 07:29 PM

That a great question- I will have a heat pump for primary heating, the radiant floor is just to keep my wife's feet toasty.

warmsmeallup 05-21-2012 08:05 PM

Technically, yes, the slab will pull some heat downward. However, if the element is in the mortar for the tile itself, it will not be ineffective at all. In fact, you should get reasonably fast reaction times.

Will the system cycle more often than if you installed an insulator or thermal break below, yes. However, the only real way to prevent it would require you raising the floor level at least an inch to accomodate the 3/8" polystyrene insulator and 1/2" backer board you'll need. On the other hand, make your wife happy, and you'll be smilin' in the end. :thumbup:

Now, granted, the island has some of the highest EL rates in the nation. Take out your dec-jan bill and divide the TOTAL of the bill by what your kilwatt hour usage was for that pay period. That should give you something like $0.20 +/-. Then let me know that info and which system you plan to buy in a private message and I'll get back to you with costs.

MikeDobbs 05-21-2012 08:26 PM

I'll get that info and get back to you- thanks very much!

Dennis Schramel 05-22-2012 02:03 PM


We always recommend insulation on top of a concrete slab. However, any insulation is better than none at all. Cork works well but we would recommend a thermal insulation panel made by Fin Pan. The 3'x5' insulated cement board is called ProPanel and it is only a 1/4" thick and very lightweight. Installation is done by bonding the panel to the slab with thin set mortar. The problem with finding a ProPanel distributor near where you live. The product is oversized for standard UPS shipments. Good luck

MikeDobbs 05-22-2012 06:55 PM

Thanks Dennis- that sounds like it might work great- I'll look into it

warmsmeallup 05-23-2012 09:11 AM

Interesting product Dennis. It definitly has it's benefits over the 3/8" roll out poly from NOFP. You are right though, they don't have a real distribution network set up yet.


biggles 05-23-2012 10:04 AM

this is suppliment magazine i get with Plumbing & Mechanical magazine during the heating seasons...are you in a Levitt house..i'm down in Lindenhurst...even check out YOUTUBE on installs might catch something thing is you have to put something to reflect that heat up. produced heat always goes to the coldest temperature....if your local to me stop by i'll give you the magazine....dated 2011

warmsmeallup 05-27-2012 12:33 PM

I'm guessing that the term may have been used incorrectly and I don't mean to get over techinical about it but you can't "reflect" heat up in a slab. You can add resistance on one side of the heat to help direct it to follow an easier path (which, in this case, we hope is upward) but a "reflector" is only used when there is an air gap betrween the heated surface and the insulation.

A "reflector" in contact with a concrete slab becomes a conductor.

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